Hi I am a bit of a noob with an Alienware so bear with me here

Ok, so i bought an Alienware 14 laptop (the 2013 model I'm pretty sure) last weekend so it came in the mail and everything was good and transaction was perfect except for one thing. (I bought it off Ebay btw) In the description he put battery has been replaced but the problem is the batter should last at least a little longer than it does. I looked it up and it should around last 5 hours  but mine only lasts 1 hour and 30 minutes. That **bleep** because I want to use it at different places on the go and hey 5 hours is OK by me by 1 hour... no. Maybe the guy i bought it from was lying but everything else was perfect so I don't think that's what happened. I wanted to use it without having to charge it everywhere I go like a PC.

Please help!